Manufacture of slidable-core pencils



Sept 8, 1959 E. LoRENlAN 2,902,754`

MANUFACTURE OF SLIDABLE-CORE PENCILS Filed July 2, 1956 3 Sheets-Sheet 1 FIG.I

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' MANUFACTURE oF sLmABLE-CORE PENCILS Filed July 2, 195e 3 sheets-sheet 2 FIG."

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MANUFACTURE 0F SLIDABLE-CORE PEINCILS Filed July 2, 1956 3 Sheets-Sheet 3 FIG.22 F|G.23

United States Patent MANUFACTURE F SLIDBLE-CORE'PENCS Eugenia Lorenan', Hamburg, .Germany Application July 2', 19556, S'eraI'No. 595,454y

Claims priority, applicatonGermanyJuly 7,1955'- 11 Claims. (Cl. 29`417) My invention relates tof a method' of manufacturing slidablecor`e pencils by extrusion and' to thel products made thereby;

It is' known to make slidable-c'ore pencils' for writing, drafting and other markingV purposes in which the lead' or other marking core i's displaceable inthe sheath by mechanica-l pressure for restoring the Worn-off"y tip` of the markingcore. In` most ofy these pencils, a rotary screw mechanism is used for advancing and/or retracting the lead. There are also pencils whose' sheath has a longitudinal slit through which a mechanical structure penetrates into` the lead channel of the sheath for imparting the desired displacement to the core.

The conventional method of producing pencils of' this general type is to manu-facture the sheath structure separate from the lea-dv or other marking` core and to subsequently insert the lead.

It is an object of' my invention to devise a method of making slidable-core pencils which greatly simplifies the manufacturing procedure by extruding the. sheath and'. combining it with the core in a single continuous operation, and which` also results in. products different from, and in some respects superior to, the. known pencils of the slidable-cor'e type.

To this end, and in accordance. with4 one ofthe features of my invention, I extrude a: sheathmateria-l longitudinally upon and around an advancingmarleingcore medium but shape. the sheath material to linfalA shape before placing it uponv the corey medium, and.l I then deposit the shaped sheathm-ateriali ont the core material in a close sliding-fit relationv thereto-While preventing. the exertion of any radial pressure up'on `the sheath material from a` point ahead of the confluence of. core and sheath material all the wayl to-- the extrusion outlet from which th'e extruded productI continuously emerges.V asa pencil strand. In the pencil bodies Aice! According to a more specific feature of; the invention, the method is carriedl outby using a marking-core medium preferably ofi such character or composition as to'v have no welding or adhesion tendency' relative to the sheath material` under the' above-mentioned' extrusion conditions. For instance, a lead or other marking material of the ceramic type,` such as the mixture ofI clay and graphite commonly' used' for pencils, is adhesively incompatiblev withsome thermoplastic sheath materials. The use of such adhesively incompatible materials for core andl sheath. respectively greatly facilitates attaining the desired longitudinal displaceability of. the: core in the sheath.

According. to another'` specific feature ofY the invention, also applicable with: incompatible core and sheathmaterials'v but ofV particular advantage with core and sheathmaterials that tend to adhere or become welded to-each-other, I. coat the core or` core medium with a thin hlm ofantiadhesive substance prior to bringing the extrudable' sheath material,v after shaping. it to the size and shape ofthe desired'sheath, intothe tight sliding-lit engagement with the coref medium.v The ilmv coating need.l not have good lubricating qualities because it should permit axial displacement of the core only' by application of. axial pressure to4 the core but should prevent inadvertent coreA displacement' without pressure. The substance ofthe coating, therefore, may be chosen from a great variety of materia-ls including waxy and fatty substances, resinous and other plastics, as well as'viscous or iluidsubstancesuor any mixture of such. substances with' a'powdered materiali such as talc, that. is incornpatible with the sheath material.y

The materials used. for the sheath? and the c'ore are preferably sor chosen as to= be' practically insensitive to' moisture and'dryness. The core'material'. may be of the above-mentioned:ceramictype.andamayhehardcnedl prior to' applying it to the extrusion@ methodlof ther invention'. However, according to another feature of thel invention; ther core medium. may be applied: ini deformable and. extrudabley condi-tion so that' tl-re*A pencil core is ext truded under heat and pressure simultaneously with' the' type core' or acopying core.

subsequently cut off the strand, the core' is'V practically' immovable in the sheath in the transversedirection over the entire length of the core but is longitudinally displaccable if sufficient axial force isapplied. Ij therefore complete eachv individua-l pencil by adding: thereto' a mechanical, hydraulic or pneumaticr pre'ssurei means which, aswill appear from the'following, can be done ina very simple manner.

More particularly, when extruding andi shaping the sheath material around the travelling marking-core' medium in the above-described manner, I` lc'eep both separated'from eachV other by a thin-walled elongatedlnozzle tube as the sheath material, passi-ngI throughA a' tapering nozzle bore, isI being compressed and slapedtor its ultimate cross-sectional` size andy shape, before I` permit the core and sheath materials, both advancing at the same speed, to pass beyond the end of' the noz'zlethe whence they travel through a cross-se'ctionally constant outlet portion of the nozzle bore in mutually nonladl'e'ring condition and without any radial pressure` being exerted upon the sheath material.

The sheath' material' for the method and products according to the invention may consist generally of any extrudable-'and preferably non-metallic' material practically insensitive to moisture, dryness and other atmosphe'ri'c-` changes so`-th`at` it will neither expand nor shrink dueto atmospheric conditions.v I preferably'usel as sheath material a res'inous plastic; suchl as thermoplastic synthetic or natural resins or compositions containing such thermoplasticresins.. Also suitable are thermosetting' synthetic. resins or. compositions containing such' resins; When making. the core: medium by extrusion, the. core material,` likewise,` should preferably bey sucl'r as tot be free of expansion and shrinking: under atmospheric conditions, and thecore material may thenalso contain thermoplastic or thermosetting resins as just1 mentioned with reference to the sheath material..

The marking. core in pencils made according to the invention may have any desired cross-sectional shape and size. It is. advantageous to keep the core thin` and to give the cross section a non-circular shape such as the shape of`an equilateral triangle or square. Such. cores, having longitudinal edges, always permittwriting. avery thin line `without necessityY for sharpening the. protruding point ofthe core because the edges, when wearing down, always produce new sharp points.

The method according to the invention can be carried out with screw extrusion presses, generally as known, which are provided with heat control means for heating and/ or cooling the materials being extruded so as to keep them in the proper condition and convert them -to the consistency and degree of rigidity desired in the various stages of extrusion travel. Preferably used are extruslon devices with coaxial nozzles generally as described in the copending application of my husband, Zareh Lorenialn Serial No. 279,496, filed March 31, 1952, now Patent 2,790,202, for Method and Apparatus for Manufacturing Pencils. However, as will be explained, the present invention makes it necessary to modify such extrusion devices so that no radial compression of the sheath material can occur anywhere along its Way from a point ahead of the inner-nozzle outlet to the outlet of the sheath-forming outer nozzle. In this respect, the devices used for making pencils according to the present inven tion are also fundamentally distinct from all previously known proposals of extruding pencils resulting in pencils with bonded and completely immovable marking cores.

The foregoing and more specific objects, advantages and features of my invention will be apparent from, and will be mentioned in, the following description with reference to the embodiments shown by way of example on the accompanying drawings in which:

Fig. 1 is an axial section through an extrusion appa ratus for making slidablecore pencils.

Fig. 2 is a partial axial section and Fig. 3 a cross section, along line III-III in Fig. 2, of a pencil made by means of the apparatus, both figures, for the purpose of illustration, showing exaggerated thickness of a coating on the pencil core.

Fig. 4 is an axial section of another extrusion apparatus for simultaneous extrusion of sheath and core according to the invention.

Fig. 5 is an axial section of an embodiment of a pencil with hydraulic pressure means for displacing the core; Fig. 6 is a similar illustration of a pencil modified by means for preventing reverse travel of the core; and Fig. 7 shows the latter means separately in perspective illustration.

Fig. 8 is a sectional view of another pencil made according to the invention and provided with pneumatic core-displacing means.

Fig. 9 shows in section a further embodiment of a pencil with mechanical core-displacing means; Fig. l is a cross section of the same pencil; and Fig. 1l shows the displacing means separately and in perspective.

Figs. l2 and 13 are partial and sectional views of still another embodiment showing mechanical core-displacing means in released and latched condition respectively; Fig. 14 is a top View and Fig. l5 a perspective View of the same displacing means.

Figs. 16 and 17 show part of another pencil with mechanical core-displacing means in released and latched condition respectively; and Fig. 18 is a separate perspective view of the same means.

Fig. 19 is a partial, sectional view of a further pencil with mechanical core-displacing means according to the invention; Figs. 20 and 2l are partial side views of the same pencil with the displacing means in released and latched condition respectively; Fig. 22 is a perspective view of the same means; and Fig. 23 is a cross section of the same pencil.

In the apparatus shown in Fig. l, rigid pre-formed leads 1, such as ceramic graphite mixtures, are used as the pencil-core medium. The leads are supplied, abutting against each other in a continuous sequence, through a nozzle inlet pipe 2 secured by a nut 3 to the body 4 of an extrusion nozzle of the cross-head type. The pipe 2 is counterbored at its discharge end to receive the inlet part of an inner nozzle which comprises, adjacent to part 5, a long and thin-walled nozzle tube 6 whose bore 4 has a cross section of circular or non-circular shape corresponding to that of the leads passing through the tube.

The sheath 7 of the pencil is produced from plastic material as described above. The plastic material passes through an outer-nozzle bore and, during manufacture, is in plasticized condition in the more portion denoted by 8. The outer-nozzle bore has a portion 9 which symmetrically surrounds most of the length of the innernozzle tube 6 and tapers toward the inner-nozzle outlet of tube 6 so that the sheath material, being extruded along the core material, is shaped to its final shape while being kept separate from the core 1 by the tube 6. Any damage to the core medium due to the shaping action is thus prevented as well as any mutual adhesion or coalescence of sheath and marking medium.

The outer-nozzle bore further has an axially elongated end portion 10 of constant cross section corresponding to that of the finished pencil sheath 7. The outlet 11 of inner tube 6, where the wall of the tube 6, tapers down to a line edge of the cross sectional size of the core, is located within the constant Width portion 10 of the outernozzle bore at a point so far remote from the narrowest cross section of the tapering bore portion 9 that radial pressure is no longer effective in the sheath material. On the other hand, the tube outlet 11 must also be spaced axially from the outer-nozzle outlet to secure satisfactory burnishing of the sheath and secure complete and definite shaping of the sheath to its final size about the slidable core. As a rule, therefore, the inner-tube outlet 11 is preferably spaced from the outer-nozzle outlet a distance larger than the width of the emerging sheath 7 but smaller than the axial spacing of tube outlet 11 from the narrowest cross section of the tapering bore portion 9. In this respect, the apparatus differs from those disclosed in the above-mentioned copending application Serial No. 279,496, now Patent No. 2,790,202.

The tapering bore portion 9 and the constant-width bore portion 10 of the sheath-forming, outer nozzle form part of a nozzle insert 12 secured to cross-head body 4 by means of a nut 13. The body 4 has a threaded nipple portion 14 screwed into the discharge end of the cylinder 15 of a conventional screw press whose press screw 16 forwards the sheath material into and through the nozzle. Electric heaters 24, 25, 25a surround the press cylinder 15 as well as the nozzle body 4 and the nozzle portion 12 for keeping the sheathing material in proper condition until the pencil is formed. Channels 26 are also provided in the body 4 for coolant or temperature-controlling medium which is introduced through an inlet port 27 in a sleeve 28 welded to body 4 and is discharged through an outlet 29 in the same sleeve. The coolant or temperature-controlling medium serves to properly set the sheathing material so that, as the extruded strand leaves the discharge end of nozzle portion 12, the sheath 7 is completely shaped and envelopes the lead with the desired close but sliding fit.

In cases where the marking-core medium consists of a material incompatible with the plasticized sheath material so that undesired Welding or adhesion of core to sheath does not tend to occur, no further equipment is needed for performing the method of the invention; but if such tendency exists, the core medium is preferably coated with a film of a waxy, fatty or other adhesionpreventing substance. For this purpose, the device of Fig. 1 is shown equipped with an auxiliary nozzle device comprising an inlet pipe 31 through which the coating substance is supplied to a nozzle chamber 32 surrounding the incoming core medium within the inlet pipe 2. Pipe 31 is threaded into a hole in the side of pipe 2. A very fine film coating, for instance of stearine or high-boiling mineral grease or silicone grease, is sufficient to make the surface of the core medium incompatible or non-adhesive in the above-mentioned sense.

The pencil strand thus produced, and the individual pencils cut therefrom, are as schematically shown in Figs.

2 and 3 where the coating on core 1 is. denoted by 1 and, as mentioned, is purposely shown with exaggerated thickness.v Actually, the film. may be made so thin that it does not noticeablyv increase the diameter of the core.

An apparatus generally asy shown in Fig. l` is. also suitable for producing the marking core by extruding a plastic core medium simultaneously Wit-h the above-described extrusion of the sheath` material. For this purpose it is only necessary to forward and extrude the marking- Core medium by means of another extrusion press, for instance also of the screw type, through the core-nozzle inlet pipe 2. Another apparatus suitable for a similar method is shown in Fig. 4 and described presently.

The apparatus shown in Fig. 4 serves. for making a pencil where both the marking material4 and the sheath are thermoplastics. Two feed'screws are, arranged concentrically to one another, the inner one. 33 serving for feeding the thermoplastic marking material` 34 which is formed in the inner nozzlel 35 into the lead of the pencil. TheY nozzle 35 has a sleeve 36 surrounding the screw 33 and, welded or screwed to the lower endV of nozzlev 35. The outer screw 37 serves for feeding the sheathing ma,- terial. 38,. and` operates in` the nozzle 39 |which is. mounted in a sleeve 40. The inner nozzle 35 terminates in a long, thin-walled tube 41 arranged within a; constantwidth portion 42 of the outer nozzle in accordance with the, same principles as explained above with reference. to Fig. l. Located between sleeve 36. and nozzle 35. is a channel 4,3 for temperature-controllingv medium. Between nozzle 39 and sleeve 40. there is also a. channel 44 for temperature-controlling medium. Denotedv by 45 and 46. are thev inlet and outlet, respectively, of channel 44. The bore of nozzle 35. is shaped. to receive' the feed screw 33 and* tapers gradually tothe desired diameter of the finished pencil lead. The `bore of the: outer nozzle in Fig. 4 is shaped similarly to the outer nozzle shown in Fig. l sothat the thennoplastic sheathingmaterial- Hows over the nozzle tube 41 and covers the leadv emerging from. nozzle tube 41V smoothly in slidingffty engagement and.` without any radial pressure.

As mentioned above, the strands. made in the= described manner, for instance with4 the aid of machinery as described with, reference toligs. l` and4', are; subsequently subdivided into individual, pencil, bodies; which. are then equipped, .with pressure means, for displacing theV core relative tothe pencil, shea-th., rlhis will now be described more in detail with reference. toY the. pencils illustrated in Figs. 5 to 23'.

Referring lirst to Fig. 5, thel individualpencil bodies, eachA comprising a, sheath Si). enclosing a.y marking core 5l which. is displaceableonly in. its longitudinal direction under application of pressure, are first given a conical taper 52,.at one end of the body.` This can be done, for instance, by means of a` pencil. Sharpener. For that reason, the plastic sheath materialis prefer-ably made of such` a compositionthat the, finished sheath is scissible.

According to Eig. 5,thezopposite end, 53 of the, pencil sheath isrnachined` to al somewhat.- smaller diameter and is. provided with a. screw threadA 54;, The core channel 55 of the sheathY is. preferably. widened` at 56 tol provide together with` the-interiorof an interiorly threaded sleeve 57. a suciently large space 58- for the reception` of a hydraulic medium.. The sleeve 57.` is in tight threaded engagement with the end portion 54 of the sheath The hydraulic medium ii'lls` the space. 58 aswell as, the, adjacent conical bore 56 of the channel: 55.. By turning the sleeve, 57, the core 51 can be madeto protrude more or less, out of the conical portion 52 of the sheath and, if desired, may also,b e retracted intothe4 sheath by turningA the sleeve in the opposite direction and pressing the core back into the channel.

Fig.` 6; shows. a similar pencil with, hydraulic, pressure means. correspondingA to, those shown, in, Fig. 5 as is apparent. from the use of the same reference numerals in both guresfor respectively similar elements. However,

lthepencil according to-Fig. 6 is provided with a Iatching `insert-,63 adjacent toY the core'51- in the channel 55 of the sheath- 50. The insert 63 is separately illustrated in Fig. 7'. It consists ofa smallv body of metal or plastic whose cross section-corresponds tot-hat; of the core channel. The body' is. squared off Vat and, at this location, is provided with-two-barbs; Whichextend to the rear and are curved outwardly. As a result, when the marking core S1 is advanced by turningV the pressuresleeve S57, the barbs 65 slide along thechannelA 55 andwhen backpressure is exerted upon the; core 5l,` enter into the material of the sheath 50- and thus latch thecore, in position. As a result, the core cannot be retracted, but the latch body 631 provides a rigid abutmentv to.- prevent undesired yieldingof the.: writing tip back into. theA sheath when using the pencil. The l'atching'A body 631 may either be placed loosev beside the cereSlV or it'may' be bonded', thereto.

When referring herein to hydraulic pressure means. this. term is, meant to. include any positive displacement means; operating with a; ilowablemedium` regardless of its particular type. Thus the hydraulic medium may consist, Vfoninstanee, of water, oil, paste,A grease, waxy material,A and: gliding ,organic or inorganic pulverulent and granular' substance whichby means of any suitable pressure-applying.r device. acts. upon the.- marking; core in a direct or indirect manner.

The: pencil; illustrated in4 Fig. 8; is similar to those of Figs.,5'y andl 6, but is equipped. with pressure means of the Pneumatic` type. Mounted: o n-` the top, end of the pencil sheath-551it is` a cap 66 to serve as; a cylinder: A plunger 67 adjacent to a pushbuttnn 6.8 has a tting or sealv 67a and is axially displaceable. in the cylinder sleeve 66' togethen with,V seal 67a. Plungen and seal arek vnormally biased by a, helical. compression spring 69v tothe illustratedposition, The cylinder; sleeve 66=has near its top endf a lateral. borel 66a throughfwhich. it' communicates with the. atmosphere. Each. time the; button. 618 is depressed, an amount of air is compressed. and-forced into the corechannel 5.5, thus advancing thecore 51 together with a latchinginsert 63 the latter being in4 accordance with; Fig. Aften each` such, actuation, the'l plunger 67 and'` the seal 67a; are returned into. ther illustratedposition by the action of; spring 69. During the returnrnovement the air behind the plunger'escapesthrough the bore 66a VorV also; throughA the gapibetwcen sleeve; 66 and pushV buti ton 68. Thereafter, the push button 68 is again readyfor actuation; By virtue of;the.latching eiiectcaused by the insert; 6 3', the; pencil' core- 51. is: not retracted`r during; the return. movement o f plunger'67 and seal 67a.

The terrrr. pneumatidas used herein is meantv to, refer toi pressure;y actuation; by,` any compressible. medium, thus, aside fram atmospheric air, .the pneumatic pressure for displacing the core may. also-be applied;v forl instance by meansof. pre-compressed: air; bynanv other. gas under atmospher-,ic or; non-atmospheric pressure;` ai substance that is liquid when compressed and gaseous; when in nonfcompressed condition, which lby means;l ofi anyy suitablepressure-applying device. acts directly or indirectly upon the marking: collez..

The; pencil; illustrated in Figs.I 9ftox lll, as well; as those shown in all subsequent illustrations, is; equipped: with; a purely mechanica-l' device: fonanplyi'ng displacing-'pressure to thapeneil core.l Thepencilsheath. 50;'is provided with a thin slit which extends over the cylindrical portion ofthe, vindivi-dual4 pencil. hun not over thefconical` end porti0u152.Y and whichinenetnates; down to the marking core orcore. channel;y The slit. Zllimay be. produced, prefer.- ably, by meansgo athinicircular; saw, after the.- individual pencilnbodics are, cui: citt the strand.emerging,y from the extension; apparatus.. Preferably,` however, the slit is cutinto; the: strand shortly, after itsaextrusion so that the slitting operationl forms ai step oa continuous fabricatingprecessfandistfollofwed'bythe cuttingoperation which likewise tonus.. a Vstep- Qfthe. sameprocess. More specilicalhasuch a-.continuous operation ist periormed'. by slitting the pencil strand during itsY travel over a given axial length, then skipping another strand portion so that no slit is produced in the latter portion by the saw or other slitting tool, then repeating the slitting operation over the same given axial length before the slitting tool again skips another portion of the strand length. The strand is then cut into pencils at respective points of severance located in the un-slitted portions which are subsequently machined to the conical tape 52 at the writing end. It will be recognized that in such continuous manufacture the slitting operation and severing operation are intermittently performed on the continuously travelling strand.

According to Figs. 9 and 10 a sleeve 71 is slidably mounted on the pencil sheath 50. As separately shown in Fig. 11, the sleeve 71 has a thin-walled extension 72 which projects inwardly through the slit 70 into the core channel 55 (Fig. 9) of the pencil sheath. The extension 4abuts against the marking core 51 so as to advance the core when the sleeve 71 is displaced toward the left in Fig. 9. Mounted on the extension 72 are barbs 73 which pierce into the material of the sheath 50 when back pressure is exerted upon the core and thus prevent the sleeve 71 and the pencil core 51 from moving backward.

The pencil shown in Figs. 12 to l5 is likewise provided with a longitudinal slit 70 extending along the sheath 50 down to the end portion 52; but is equipped with a dif- 'ferent core-displacing mechanism. This mechanism, separately shown in Fig. 15, has an inner portion 75 whose circular or polygonal cross section corresponds to that of the core channel. The portion 71 is connected with an outer portion 76 of the device by means of a thin web 77 which, in the assembled condition of the pencil, extends transversely through the slit 70 in the pencil sheath 50. The web 77 is preferably provided with a hole at 78. A pin 79 is slidably mounted in portions 75 and 76 and forms a stop at 80 which limits the displacement of the pin so that the pin cannot inadvertently be pulled entirely out of the device. The pin carries a knob 81 on its outer end and is sharpened to a point at its opposite end 82. When pin 79 is retracted by pulling knob 81 to the position illustrated in Fig. l2, the slide mechanism is displaceable to shift the pencil core. When the knob 81 is pushed in, as shown in Fig. 13, the point 82 of pin 79 pierces into the material of the sheath 50 and then locks the mechanism as well as the marking core in the proper position.

The modified core displacing mechanism illustrated in Figs. 16 to 18 has an inner portion 85 slidably disposed in the core channel 55 of the sheath 50 and joined with an outer portion 86 by a thin web 87 which extends through the longitudinal narrow slit 70 of the pencil sheath f). A lever 88 is pivoted at 89 to the outer portion 86 of the mechanism. The lever 88 preferably consists of a sheet metal structure of a channelshaped cross section and is provided with one or two pointed projections 90. When lever 88 is in the releasing position shown in Fig. 16, the mechanism can be displaced along the pencil sheath in order to push the marking core 51 a desired amount out of the tip of the sheath. When the lever 88 is placed into the position shown in Fig. 17, the tooth or teeth 90 pierce into the material of the sheath on both sides of the slit 70 and thus latch the mechanism and the core S1 in position.`

The pencil according to Figs. 19 to 23 is provided with a sleeve 91 which is slit longitudinally to act as a spring and is displaceably seated upon the sheath 50. The sleeve 91 has a number of outwardly and downwardly increasing wedges 92 located in the lower portion of the sleeve. A ring 93 is slidable on the upper portion of the sleeve and can be forced downward over the wedges 92 from the position shown in Figs. 19, 20 to the position shown in Fig. 21. This has the effect of clamping the sleeve 91 against the sheath thus securing the sleeve in xed position. It will be recognized that, as far as described, the sleeve mechanism is similar to known clamping devices used on conventional pencil holders of sheet metal. However, for the purpose of the vpresent invention the device is modified as follows. Joined with the sleeve 91 is a web portion 94 (Figs. 22, and 23) which passes through the narrow slit 70 of the pencil sheath and carries a dowel portion in the core channel 55 (Fig. 19) of the sheath. Consequently, when the ring 93 is shifted to the releasing position of Fig. 20 and the sleeve 91 is forced downwardly, the pencil core 51 is pushed forward to provide a new writing tip. Thereafter the sleeve 91 is clamped by shifting the ring 93 to the position of Fig. 2l thus locking the pencil core 51 in proper position.

It will be recognized from the various embodiments described in the foregoing, that the invention is applicable for producing a great variety of different pencil designs. As also embodied in the examples described, such pencils can be given largely the appearance of ordinary wood-sheathed writing or drafting pencils to be used in such a manner that the pencil can be discarded when the entire marking core is consumed, the manufacture according to the invention being so much less costly than the conventional methods of making slidable core pencils as to make such use of the pencils economical. That is, such slidable-core pencils can be manufactured at no greater cost than that of conventional wood-sheathed pencils with the added advantage that they require no sharpening and do not become shorter by wear. However, if desired, the method according to the invention is also applicable for the production of more elaborate sliding-core pencils with any desired, more or less fanciful displacing mechanism which then, of course, may affect the cost of the pencil. Furthermore, the invention is not limited to disposable pencils but can also be used for the production of pencils with replaceable marking cores, for instance, of the ordinary ceramic-lead type.

The manufacturing method according to the invention can further be supplemented by an additional method step for the purpose of controlling and, if necessary, correcting the proper engagement of the pencil core with the sheath. For instance, it may happen that the sliding fit engagement between core and sheath after extruding the pencil strand and cutting it into individual pencils is not such as to permit a displacement of the core only under pressure. In order to correct this, the pencils, after being cut from the strand and after having been given a conical writing end, may be inserted under pressure and in heated condition into a conical gauge which may also be heated. As a result, the sheath material is slightly compressed at least along the conical portion 52 (see Fig. 5) of the sheath so that the engagement between core and sheath attains the proper condition in the tip portion of the pencil.

It will be obvious to those skilled in the art, upon a study of this disclosure, that the method of making slidable-core pencils as well as the pencils resulting from the method in accordance with my invention can be modified in various ways and may be incorporated in embodiments other than those specifically illustrated and described, without departing from the essence of the inven tion and within the scope of the claims annexed hereto.

I claim:

1. The method of making slidable-core pencils which comprises continuously advancing a marking-core medium in a given direction, continuously extruding a sheath material in the same direction along and around the traveling core medium and shaping said material into substantially final shape while maintaining it separated from said core medium, then placing during further travel the shaped sheath material around the core medium with slight but sufiicient radial clearance to maintain the shaped sheath material in sliding-fit engagement with said core medium while passing the sheath material through a nozzle having constant inner cross section from aheadof the first meeting point of said medium and said material to the nozzle outlet point,y said core medium being adhesively incompatible with the; shaped sheath material, whereby in the finished pencil the core is practically immovable radially in the sheath but is longitudinally displaceable by application of pressure.`

2. rlhe method of making slidable-core pencils,1 which comprises advancing a marking-core medium through an elongated thin-Walled tube, extiuding a plastic ,Sheath material along the tube and shaping said material symmetrically around the tube to the, substantially inalshape of the pencil sheath while maintaining core medium and sheath material separated from each other by the thinwalled tube up to a point where said final shape is attained, and then continuing the extrusion of core medium and sheath material through an elongated nozzle outlet bore of constant cross section while maintaining a slight but sucient radial clearance to maintain the shaped sheath material and the core medium in sliding-tit engagement with each other, said core medium being adhesively incompatible with the shaped sheath material, whereby the pencil strand issuing from the outlet bore has the core practically immovable radially in the sheath and slidingly displaceable in the longitudinal direction only by application of pressure.

3. The method of making slidable-core pencils by extrusion through coaxial nozzles, which comprises continuously forwarding a marking-core medium through an elongated thin-walled tube forming part of the inner nozzle and having an outer cross section corresponding nearly to that lof the marking core, extruding a plastic sheath material along and around said tube and shaping it internally andexternally to substantially iinal shape as it passes along said tube, said core medium being adhesively incompatible with the shaped sheath material, maintaining the sheath material coni-ined to a constant cross section from a point along said tube to the outernozzle outlet, said outer-nozzle outlet being axially spaced from the tube outlet a distance larger than the sheath diameter but smaller than the axial spacing of said tube outlet from said point so that the sheath material is no longer subjected to radial shaping pressure in the entire zone wherein the core medium travels together with theV sheath material, depositing the sheath material in said zone on the core medium While maintaining a slight but sufficient radial clearance to maintain the shaped sheath material and the core medium in sliding-tit engagement with each other, whereby in the pencil strand issuing from the outer-nozzle outlet the core is practically immovable transversely of the sheath but is axially displaceable by application of pressure.

4. The method of making slidable-core pencils by extrusion through coaxial nozzles, which comprises continuously extruding a thermoplastic marking-core medium through an elongated thin-walled tube forming part of the inner nozzle and having an outer cross section corresponding nearly to that of the marking core so that the core medium issuing from said tube has the shape of the nal pencil core, extruding a thermoplastic sheath material along and around said tube and shaping it internally and externally to substantially iinal shape as it passes along said tube, maintaining the sheath material conlined to a constant cross section from a point along said tube to the outer-nozzle outlet, said outer-nozzle outlet being axially spaced from the tube outlet a distance larger than the sheath diameter but smaller than the axial spacing of said tube outlet from said point so that the sheath material is no longer subjected to radial shaping pressure in the entire zone wherein the core medium travels together with the sheath material, said core medium being adhesively incompatible with the shaped sheath material, depositing the sheath material in said zone on the core medium while maintaining a slight but suicient radial clearance to maintain the shaped sheath material and the 1'0 core medium. in Sliding-ft. engagement with each other; whereby in the pencil strand issuingA from. the: Centernozzlre outlet the core Iis, practically-immovable trans,- verselfy Qf the sheath but is. axially displaceable by application ofA pressure. Y' A 5i., The method of slidable-core pencils, which comprises continuously advancing a marking-core medium in a given'direction, continuously extruding in the same direction along and around the travelling core medium,- a non-metalli? d.eliornfiableV sheath material practicallyy insensitive-A tompisture. andi dryness and shaping said sheath material into iinal shape while maintaining vit separated from said core medium, then depositing during further trfaxe1z-thesbapedgshaath matcrialtunnniand around the core medi-nin in sliding-.fit engagement ltherewith and with slight radial clearance while passing the sheath material through anozzlehaving-constant inner cross-section from ahead of the rst meeting point of said medium and said material to the nozzle outlet point, said core medium being adhesively incompatible with the shaped sheath material, whereby in the finished pencil the core is practically immovable radially in the sheath and is longitudinally displaceable only by application of pressure.

6. In the method of making slidable-core pencils according to claim 1, said marking-core medium being adhesively incompatible with said sheath material, whereby bonding of core medium to sheath material in the finished pencil is prevented.

7. The method of making slidable-core pencils according to claim 1 wherein the core medium as such is adhesively compatible With the sheath material, comprising the step of coating the core medium with a lm of adhesion preventive substance prior to depositing said sheath material onto the coated core medium, whereby bonding of core medium to sheath material is prevented and the core remains displaceable by application of pressure.

8. The method of making slidable-core pencils which comprises continuously forwarding a marking-core medium in a given direction, continuously extruding a sheath material in the same direction along and around the travelling core medium and shaping said material to a pencil sheath, depositing during further travel the shaped sheath material upon the core medium while maintaining a slight but suiiicient radial clearance to maintain the shaped sheath material and the core medium in sliding-t engagement with each other so as to obtain a pencil strand, said core medium being adhesively incompatible with the shaped sheath material, severing individual pencil bodies oi the strand, and attaching to each body a means for displacing the core relative to the sheath.

9. The method of making slidable-core pencils according to claim l, which comprises the steps of slitting the sheath material longitudinally `down to the marking core medium over a given axial length as the pencil strand is emerging from the nozzle, interrupting the slitting operation for another given axial length of the strand, cyclically repeating both steps and cutting the strand into individual pencils at respective places each Within one of said latter axial lengths, whereby each pencil has a longitudinal slit over most of its length with the exception of an end portion.

10. The method of making slidable-core pencils according to claim 1, which comprises providing the pencil strand, prior to severing the individual pencils from said strand, with thin longitudinal slits down to the core medium, each slit having a given axial length and being axially spaced from the adjacent slit, mounting the displacing means on the sheath of each individual pencil in slidable relation thereto and passing part of said means through the slit into engagement with the pencil core.

1l. The method of making slidable-core pencils, which comprises continuously forwarding a marking-core medium in a given direction, continuously extruding a sheath material in the same direction along and around the travelling core medium and shaping said material to a pencil sheath, depositing during further travel the shaped sheath material upon the core medium while maintaining a slight but suflicient radial clearance to maintain the shaped sheath material and the core medium in slidingt engagement with each other so as to obtain a pencil strand, said core medium being adhesively incompatible with the shaped sheath material, severing individual pencil bodies oif the strand, and attaching to one of the ends of each individual pencil a fluid pressure means communicating with the interior of the sheath to impose axial pressure upon the core medium for displacing said medium in said sheath.

References Cited in the tile of this patent UNITED STATES PATENTS 253,822 Mignon Feb. 14, 1882 12 Webb Jan. 14, 1908 Will Feb. 11, 1919 Ray May 31, 1927 Kochendorfer Oct. 25, 1927 Daniels Nov. 22, 1927 Vierling Jan. 8, 1929 Cato Jan. 13, 1931 Megow Oct. 23, 1934 Jacobson June 28, 1938 Kimble et al Oct. 31, 1939 Cook June 4, 1946 Lorenian Apr. 30, 1957 

